One of the key requirements of a computer system is a place to store data. Typically computer systems employ a number of storage means to store data. One of the places where a computer can store data is in a disk drive which is also called a direct access storage device (DASD).
A disk drive or DASD includes several disks which look similar to records used on a record play or compact disks which are used in a CD player. The disks are stacked on a spindle, much like several 45 rpm records awaiting to be played. In a disk drive, however, the disks are mounted to the spindle and spaced apart so that the separate disks do not touch each other.
The surface of each disk is uniform in appearance. However, in actuality, the surface of each disk is divided into portions where data is stored. There are a number of tracks of the disk situated in concentric circles like rings on a tree. Compact disks have tracks, as do the disks in a disk drive. The tracks in either the disk drive or the compact disk essentially replace the grooves on a conventional record. Each track in a disk drive is further subdivided into a number of sectors which is essentially just one section of the circumferential track.
Disks used in a disk drive are made of a variety of materials. Most commonly, the disk is made of metal, glass or plastic. The materials from which the disk is made determines how data is stored on the disk. A plastic disk, such as those used as CDS, stores data using lasers and a laser is used to read the data back. Storage of data on a metal or glass disk entails magnetizing portions of the disk surface coating in a pattern which reflects the data.
To store data on a metal or glass disk, the disk surface coating is magnetized. In order to magnetize the surface of a disk, a small ceramic block which contains a magnetic transducer known as a "write head" (also called "write transducer") is passed over the surface of the disk. More specifically, the write head is flown at a height of approximately six millionths of an inch from the surface of the disk and is flown over the track as the write head is energized to various states causing the track below to be magnetized to represent the data to be stored.
To retrieve data stored on a magnetic disk, a ceramic block which contains a "read head" (also called a "read sensor") is flown over the metal disk. The magnetized portions of the disk induce a current in the read head. By looking at output from the read head, the data can be reconstructed for use by the computer system.
Typically, the same ceramic block contains both a read head and a write head.
Like a record, both sides of a disk are generally used to store data or other information necessary for the operation of the disk drive. Since the disks are held in a stack and are spaced apart from one another, both the top and the bottom surface of each disk in the stack of disks has a ceramic block, also known as a slider, associated with each surface. This would be comparable to having a stereo that could play both sides of a record at once. In the record analogy, each side would have a stylus which played the particular side of the record.
Disk drives also have something, called an actuator, that compares to the tone arm of a stereo record player. There are two types of actuators, rotary and linear. Rotary disk drives have a tone arm that rotates much like a record player. The tone arm of a rotary disk drive, termed a suspension assembly or a head/arm assembly, typically has one slider attached at one end. The other end of a head/arm assembly is attached to a comb-like structure. There is one head/arm assembly associated with each surface of each disk. Alternatively, two head/arm assemblies may be attached to a single arm, with the end of the arm bifurcated to accommodate a head/arm assembly for the top of the disk and a second head/arm assembly for the adjacent disk. The comb-like structure facilitates holding each head/arm assembly. The entire comb-like structure with multiple head/arm assemblies attached, is termed a head/stack assembly.
Like a tone arm, the head/arm assembly rotates so that the read and write heads in the slider which is attached to the head/arm assembly can be moved to locations over various tracks on the disk. In this way, the write heads can be used to magnetize the surface of the disk in a pattern representing the data at one of the several track locations or the read heads can be used to detect the magnetized pattern on one of the tracks of a disk. For example, the needed data may be stored on two different tracks on one particular disk, so to read the magnetic representations of data, the head/arm assembly is rotated from one track to another track. A linear disk drive, has a suspension assembly similar to that of a rotary disk drive. However, in a linear disk drive, instead of repositioning by rotation, repositioning is accomplished through linear movement.
Both the read head and the write head attached to the slider require a pair of wires to be attached to the slider itself. Thus, a typical head/arm assembly has a total of four wires. These wires are very fine and are about 0.0014 inches thick, which is about half the thickness of a human hair. The wires carry electrical signals. The electrical signals attached to the write head are used to store representations of data on one of the disk surfaces of the disk drive. The electrical signals attached to the read head are used to carry signals representing the data back from one of the surfaces of the disk which has data stored on it. A set of wires for each read head and write head are strung along each of the actuator arms in the disk drives. Each set of wires for each of the read heads and write heads typically is attached to a flexible cable which allows the suspension assembly to move while maintaining electrical connection with each of the heads on the slider. Other heads are constructed such that five wires are necessary. Still other heads are constructed with a common head which performs both read and write functions. This type of head only requires a single pair of wires to be attached to the slider.
High data capacity disk drives have very small disk to disk spacings. This leaves less room to package arms and suspension assemblies. The arm tips become very thin, more flexible and subject to undesired vibration excursions from the load beams attached to the arm tips. When two head/gimbal assemblies attached to a single arm are excited into vibration, such as from actuation input forces, from air turbulence, or from disk vibration or contact inputs, the head/gimbal assemblies in turn excite the arm tip that holds the slider and also excite each other. For example, in today's high capacity disk drives, the arm tips may be reduced in thickness to only 0.57 mm thick and made of aluminum. These small arm tips support two head/gimbal assemblies, each weighing approximately 0.12 grams. Detrimental cross talk has been observed during accessing and during track following in which the resonant frequency of one head/gimbal assembly is seen as a response on another head/gimbal assembly. This phenomenon often appears to be mode splitting, however, it actually is due to mechanical coupling of the two head/gimbal assemblies. The resulting amplitude of each head/gimbal assembly's vibration is larger because the response of one head/gimbal assembly's mode is riding up the gain slope of the other head/gimbal assembly. This phenomenon has been observed on first bending, first torsion, second bending and second torsion modes at 1300 hz, 2000 hz, 4200 hz and 5500 hz in a particular head/gimbal assembly.